Last year, Tesla promised that the Model S’s rear-wheeldrive system would handle slippery roads just as well as an all-wheel drive vehicle.But with growing competition in the premium EV and hybrid market, the companywants to stay ahead of the game in drive-lines as well as in efficiency andperformance. Tesla Motor Co.’s Model X, which was already unveiled in Detroit, is expected in showrooms in late 2014 or early next year.Joined by the all-wheel drive Model S, they will both enjoy the Version 6.0software update, which should be available to existing owners in coming weeks.This will add real-time traffic data, suspension-setting controls and ride heightadjustments.